1. Field of the Invention
The present invention relates to radiation therapy in which a radiation, such as an X-ray or a particle beam including a proton beam, is irradiated to a tumor for treatment. More particularly, the present invention relates to a positioning system and method for the radiation therapy, which is useful to perform positioning of a patient and a collimator.
2. Description of the Related Art
In radiation therapy, treatment is performed by irradiating a radiation to a tumor and damaging DNA of a tumor cell. It is therefore required to irradiate the radiation in a precise manner so that DNAs of normal cells near the tumor are not damaged. Particularly, in radiation therapy using a particle beam such as a proton beam, the beam can be concentrated to the tumor with a higher dose based on beam characteristics, whereas more accurate positioning is required. This leads to the necessity of deciding the position of the patient relative to the beam with high accuracy, and of forming radiation field as per planning.
Particle beam therapy is performed as per a treatment plan prepared in advance. However, a slight deviation occurs between the position of the tumor in the patient body and the planned setting position due to various factors. To realize positioning of the patient as per the treatment planning, therefore, it is required to precisely calculate the deviation between those two positions and to correct the position of a patient positioner by using a patient moving apparatus in accordance with the calculated deviation.
The positioning of the patient in a treatment room is first performed by making the patient fixed to an immobilization device on the patient positioner, and executing rough positioning with the aid of a body surface marker and a laser marker. Then, X-ray images of the patient are captured by using an image capturing system, e.g., two sets of X-ray equipment, in order to confirm the current patient position. Resulting X-ray images are called positioning images. The positioning images are transmitted to a positioning apparatus and are stored in a medical image server.
On a display screen of the positioning apparatus, a reference image calculated and stored in advance and the positioning image are displayed to calculate the deviation of the patient position through comparison between both the images. The calculation can be performed, for example, by a method of setting calculation points on landmarks (each landmark being selected as a location, e.g., a bone part, which is clearly recognizable) on both the images by an operator using a mouse, and calculating the deviation through comparison between coordinate values of the calculation points based on an approximation method, e.g., the least square method (see, e.g., Patent Document 1: JP,A 2000-510023 (FIGS. 6-7)), or a method of comparing pixel values of both the images and calculating the deviation based on an approximation method, e.g., the least square method, at which the sum of errors of the pixel values is minimized (see, e.g., Patent Document 2: JP,A 2004-267250 (FIGS. 8-12)).
The thus-calculated deviation (including the amount of parallel shift and the amount of rotation) is converted to a position deviation of the patient positioner through coordinate transform in the positioning apparatus and is transmitted to the patient moving apparatus. In accordance with the transmitted deviation, a patient positioner controller in the patient moving apparatus controls a patient positioner drive unit to move and/or rotate the patient positioner for correction of the position deviation, thereby completing the patient positioning.
In addition, to precisely produce the radiation field as per planning, positioning of a collimator that decides the radiation field is also required to be performed with high accuracy. Generally, the collimator is mounted in a snout rotatably mounted to a fore end of an irradiation nozzle (see, e.g., Patent Document 3: JP,U 4-58266 (FIG. 1)). It is therefore important to decide the rotational angle of the snout with high accuracy.